Guest Author - Lea Terry

Far beyond the orbits of Pluto and Neptune lies a region of icy, rocky objects. Though the existence of this region, called the Kuiper Belt, was predicted in 1950, it was not proven until 40 years later. Astronomers still don’t know much about the Kuiper Belt, but they believe it is home to several comets.

Desperately Seeking: The Kuiper Belt

The idea of the Kuiper Belt was first proposed in 1950, by Dutch astronomer Jan Oort. He believed comets came from an icy region 50,000 times farther from the Sun than Earth. A year later, astronomer Gerald Kuiper echoed the suggestion, arguing that there should be comet-like debris, remnants of the formation of the Solar System, just beyond Neptune. He believed the Solar System should have an “edge,” at which these leftover bodies should be found.

Astronomers already knew about the Oort Cloud, a large, spherical region just beyond Pluto, containing as many as 6 trillion comets. However, they soon realized there was another group of comets which behaved differently than those in the Oort Cloud. This other group, called the Jupiter family, orbited the Sun in less than 20 years, as opposed to the 200 million year orbits of bodies in the Oort Cloud. And, these comets had orbits near the plane of Earth’s orbit around the Sun, in addition to orbiting in the same direction as the planets.

The idea was strengthened in the 1980s by computer simulations of the formation of the Solar System. These simulations suggested that a region of leftover debris should accumulate near the edge of the Solar System, beyond the orbit of Neptune. However, the hypothesis remained unproven until 1992, with the discovery of 1992QB1, a 150-mile wide object near the edge of the proposed belt. The theory was further confirmed by the discovery of several similar bodies in the same area.

The Kuiper Belt, aka “The Final Frontier”

The Kuiper Belt is about 7.5 billion to 9.3 billion miles away from the Sun, and may contain millions of celestial bodies, also called “Kuiper Belt Objects,” or “KBOs.” At least 70,000 of these have diameters greater than 100 km. Lying at the far reaches of the Solar System, this disk-shaped belt is sometimes called our Solar System’s “final frontier,” and indeed, it is so far away we don’t fully understand it.

The study of Kuiper Belt Objects is a rapidly growing area, progressing both theoretically and observationally. One of the most intriguing developments is the discovery of 2002 LM60, (unofficially called “Quaoar”), a frozen world about 800 miles in diameter. Unlike most celestial bodies, Quaoar orbits the Sun in a near-perfect circle. Nearly half the size of Pluto, it is the largest of the 500 Kuiper Belt Objects recently discovered.

Because the Kuiper Belt is so distant, and its inhabitants so small, viewing this region is difficult, even with powerful telescopes. NASA’s New Horizons spacecraft, however, is set to travel to Pluto and the Kuiper Belt, and may provide new insight. Learning about this region is important to scientists, because it is believed the KBOs are left over from the formation of the Solar System, and may provide a glimpse into its beginning.